Process of making light-colored ligno-cellulose fiber



Patented Mar. 11, 1941 UNITED STATES PATENT OFFICE 'azsuas PROCESS OF MAKING LIGHT-COLORED LIGNO-C'ELLULOSE FIBER I Corporation, Laurel, Delaware No Drawing.

11 Claims.

Our invention relates tolight-colored lignocellulose fiber, and products thereof, and process of making same. Wood is the preferred lignocellulose material used, but various woody materials of annual or perennial growth can also be used.

A principal object of the present invention is the production, of ligno-cellulose fiber which. although treated with steam for a short time at high temperature, is light in color and preferably about the same color of the original wood woody material which is taken for use.

Another object consists in the provision of a process for the production of steam-exploded ligno-cellulose fiber which is light in color. Another object consists in the production oi.

light-colored board, sheet, and the like products from light-colored limo-cellulose fiber.

When wood or woody material in somewhat subdivided state, as for example, wood in small chips, is subjected alone to the action of high pressure steam, and exploded by discharge to atmospheric" pressure through a constricted orifice, the resulting finely subdivided fiber material is dark-colored to an extent depending upon the steam pressure (and the corresponding temperature) and upon the length of exposure to the action of the steam. This darkening effect is apparently caused, at least in part, by production of pyroligneous acids, including acetic and formic acids, in the steam treatment of the wood or woody material, and reaction of these acids upon other parts of the wood or woody material.

According to the present invention, chips or other small pieces of wood or woody material are first impregnated with alkaline sulfite of alkali metal such as sodium sulfite, NaaSOa, potassium sulfite, K2803, or equivalent sulfite material, with or without the addition of a small percentage of free alkali such as sodium hydroxide (NaOH) for example.

Upon steam-treating and reduction to fiber as by steam-exploding of such material so impregnated, the resulting subdivided material, of the nature of fibers and fiber bundles, which is produced in accordance with the present invention, is light in color, and after suitable"beating or other refinement, as with :1. Bauer refiner, for

example, can be made use of in the production of,

light-colored sheet, board, or other products. Only light refining is required for making board products.

Alkaline sodium sulflte is preferably used for impregnation, and use thereof without added al- Miss., a corporation of Application March 31, 1938, Serial No. 199,182

kaliwill first be described for afiording an illustrative embodiment of the invention.

When wood chips or other small pieces of ligno-cellulose I material are subjected alone to high pressure and temperature in the presence of 6 moisture and then disintegrated by explosion with steam, the pH of the resulting comminuted fiber is ordinarily in the general neighborhood of 3 to 4. With such treatment the fiber secured is much darker-colored than the original wood, and 10 the yield of fiber is relatively low, as about 70% of the chips. v

When the same treatment is given to lignocellulose material in chips or other small pieces,

with, however, the only diflerence that this mate- I rial has first been impregnated with alkali metal monosulfite material, as sodium sulfite, for example, considerable changes are noted in the resulting comminuted fiber as follows: While the pH of the material used for impregnation, as sodium sulfite,'whe'n dissolved in water, is in the neighborhood of 9 or 10, the pH of the fiber material produced is considerably less than this, as. for example about pH 5 to '8. This is, however, considerably over the pH of fiber from unimpregnated ligno-cellulose material. The comminuted fiber material made from the impregnated chips, instead of being darkened, is light in color, and is of about the same coloration as the original wood. The yield of fiber product from the impregnated chips is higher, as about 80% or more, and the degree of reduction is not so great as in the case of the treatment without the preliminary impregnation.

When the ligno-cellulose' material is treated in the first manner above described, that is, without impregnation, the relatively smallyield and the darkening of the fiber produced is'generally attributed to the production of acetic, formic and other pyroligneous acids and to the 40 reaction of such acids upon the ligno-cellulose material. p v

Without commitment to particular theory as to the precise action which takes place giving the beneficial results above described by the prior impregnation with the alkali metal sulfite material, it is believed that the radicals which wouldotherwise be productive of pyro-ligneous acids are diverted to the production of alkali metal salts of acetic, formic and other pyroligneous acids, with liberation of sulfur dioxide which exerts a bleaching or decolorizing eilect upon the fiber material produced. In any. event, the discoloring reactions which, without the impregnation, would be caused by the steam treatment, are it substantially nullified by the alkaline impregnation material. g

The impregnation of the chips or the like with the alkali metal sulfite material can be per- 5 formed in various ways, but is preferably eflected by immersing the chips or other small pieces of ligno-cellulose material in a boiling water bath containing sodium sulilte in solution, followed by immersing, the chips or pieces in a second bath, which is similar to the first but at a much lower temperature, and which acts as a chilling bath. This immersion treatment can be accomplished, for example, by means of a conveyor which takes the chip material from the chipper and delivers it to the bin from which it is to be loaded into the gun for the treatment with steam followed by explosive discharge. The impregnating solution may be supplied to move counter-currently to the travel of the chips, as for example, fresh cold solution can advantageously be supplied to the chilling bath, and the solution pumped or otherwise supplied from this bath to the hot bath through a heater.

Concentration of from about 100 to 200 grams nation bath is well adapted for making an eifective impregnation. For example, when using a 10% solution of sodium sulfltein both the hot and cold baths, chips of scuthem pine wood were impregnated with 13.5% sodium sulflte (based on dry weight of wood) by immersion in the hot bath for 2 minutes, followed by immersion in the chilling bath for 2 minutes. A second lot of similar chips were impregnated with 15.2% of sodium sulfite upon 5 minutes immersion in the hot bath, followed by immersion in the chilling bath for 5 minutes. The heated bath in each case was maintained at a boiling temperature, and the cold bath at approximately outdoor temperature. A higher percentage of impregnation was secured in the chilling bath than in the boiling bath. By varying the solution percentage, speed of chip travel and dimensions of the bath containers, substantially any desired percentage of impregnation can be secured, as from 5% up to about-30%.

To securev best results in production of finely subdivided ligno-cellulose which is light-colored when treating and exploding with steam, the

gun for steam treatment and explosion of the impregnated ligno-cellulose material, containers for bath solutions, and other apparatus, which could cause discoloration of. the material by means of rust or the like, are preferably of ma- 5:; terial resistant to rust and corrosion, such as rustless steel, for example.

with as little as 5% uptake of sodium sulfite (based 'on dry weight of wood), the impregnated wood chips exploded after 30 seconds exposure to steam at 600 lbs. per sqflin. to 5 seconds expo-- sure to steam at 1000 lbs. per square inch, produce a fiber which is practically unchanged in color from that of the original wood. The percentage of impregnation of the ligno-cellulose material with sodium sulfite-or other alkali metal sulfite is preferably regulated to supply the approximate amount of the sulfite material needed to combine with the acid materials which are present or developed. when the chips are treated with steam and exploded by means of steam, the pressure of to explosion to eif ect higher subdivision upon the explosive release. I

The best results and lightest-colored fiber and products such as sheets, boards, and the like are to be obtained with hardwood chips, such as ash, 5 bay, sweet gum, black gum and tulip poplar or magnolia, and when using hard woods, the chips are preferably impregnated with an amount of ing a higher pH'value.- Soft woods, such as spruce, southern pine and cypress, can also be 20 used, and with soft woods the amount of impregnation material to be used to secure light-colored fiber is preferably regulated to yield an exploded fiber material which is slightly on the acid side,

asa pH of approximately 6 produces the lightest 25 colored fiber and pulp products from woods of this type, the'resinous materials, such as rosin, for example, normally present in such wood being capable of being saponiiied or otherwise reacting with alkali metal sulfitm in an alkaline medium 30 to form discoloring bodies.

The exploded or otherwise finely subdivided ligno-cellulose material is preferably washed for removal or reduction of water-soluble materials, including sodium acetate and sodium formate in 3 the case where sodium is the alkali metal of the sulflte. The subdivided material is self-bonding under heat and pressure and in fiber board making does not require addition of extraneous binding agents, though binders may be added if de- 40 sired. Addition of a small proportion of water-. proofing material, as 3% of petrolatum, or of rosin-alum size, for example, is useful for enhancement of the resistance of the products made from this material to absorption of water. 45

The light-colored ligno-cellulose fiber produced as described may be formed into sheets and consolidated under heat and pressure in any known manner, as for example in the manner described in the U. 8. Patents to Mason Nos. 50 1,663,503, 1,663,504 and 1,663,505, and the fiber board products produced in this and other ways are little if any darker than the original w or other ligno-cellulose material. 1

The following examples show a comparison of results obtained with the hard wood,- bay wood, when steam-exploded without and with the addition of sodium hydroxide. Bay wood in small chips, after immersion in hot and cold baths respectively of water solution of sodium sulfite of an about 9.6 pH, had an uptake of about 7% sodium sulfite. This chip material was placed in the gun and the steam pressure was raised in a period of 30 seconds to 600 pounds per square inch. The steam pressure was then raised in a period as of 5 seconds to 1000 pounds per square inch, and after this pressure had been held for a period of 5 seconds, the material was exploded from the pressure of 1000 pounds per square inch. The finely comminuted fiber material obtained was 70 fairly white in color, and had a pH of 5.3.

Another lot of bay wood material in small chips was treated in the same way, except that sodium sulfite and sodium hydroxide was used in the impregnation baths in the proportion of one part sodium hydroxide to six parts sodium sulfite. The pulp obtained was very light in color and had a pH of about 8.2.

While the ligno-cellulose material in the form of small chips may be dried or partially dried after impregnation, and then treated with steam and exploded, the best results and lightestcolored products are obtained with the introduction of the material into the steam treating and exploding gun, without drying after the impregnation treatment, and containing in the general neighborhood of about 60% water.

In the two examples just given, the chips were taken direct from the impregnation bath without preliminary drying and the steam treatment given was adapted to such conditions. Less steam treating is required where the chips are dried after impregnation, but in any case the time of steam treatment needed for production of fiber adapted for making of fiber boards is so short that digestion of the ligno-cellulose by the impregnating material during such steam treatment is substantially avoided and the action of the impregnating material is substantially confined to releasing sulfur dioxide to act as a bleaching or decolorizing agent, and to nullifying the discoloring reactions which would. otherwise be caused by the action of the steam on the lignocellulose even in such short time.

It is to be understood that modification may be resorted to within the scope of the appended claims.

We claim:

1. Process of making steam-exploded fiber, which is light-colored and adapted for production of light-colored fiber board-s, from wood or woody ligno-cellulose material, which consists in impregnating such material in small pieces,

such as chips, with about 545% of alkaline sulfite of alkali metal, subjecting the impregnated ligno-cellulose material to the action of steam at a pressure of over 300 lbs. sq. in. for a time so related to the steam pressure used that upon explosive discharge as hereinafter set forth, it will be disintegrated to fiber adapted for manufacture of fiber boards, while utilizing the said sulfite impregnating material to combine with acids as they are developed by the action of the steam on the ligno-cellulose together with production of sulfur dioxide serving as a bleaching or decolorizing agent, and disintegrating said material by explosive discharge from the region of high steam 5 pressure to a region of substantially atmospheric pressure, whereby discoloring reactions are substantially nullified, and the ligno-cellulose ma-" terial is disintegrated into light-colored fiber.

2. Process as in .claim 1, and wherein the lignocellulose material is subjected to and exploded from steam pressure of about 1000 lbs. pressure per sq. in. and the period of subjection to steam at such pressure is approximately 5 seconds.

3. Process as in claim 1, and wherein the alkaline sulfite of alkali metal content of the chipsis adjusted to give fiber of approximately '7 pH.

4. Process as in claim metal is sodium.

5. Process as in claim 1, and wherein the alkali metal is sodium, and the alkaline sodium sulflte content of the chips is adjusted to yield a. fiber product of approximately 7 pH.

6. Process as in claim 1, and wherein the 25 alkali metal is potassium. v

7. Process as in claim -1, and wherein the lignocellulose material is hard wood, and about onesixth of the impregnation material is free alkali.

,8. Process as in claim 1, and wherein the ligno-cellulose material is hard wood, and about one-sixth of the impregnation material is sodium hydroxide.

9. Process as in claim 1, and wherein the ligno-cellulose material is hard wood, the alkal line metal is sodium, and about one-sixth of the impregnation material is free alkali.

10. Process as in claim 1, and wherein the ligno-cellulose material is hard wood, the alkaline metal is sodium, and about one-sixth of the impregnation material is sodium hydroxide.

11. Process as in claim 1, and wherein the uptake of theimpregnating material is approximately 7%;

1, and wherein the alkali 45 HOWARD W. MORGAN. BASIL O. STEWART. 

